F. K. Kong MA, MSc, PhD, CEng, FICE, FIStructE, R. H. Evans CBE, DSc, D ès Sc, DTech, PhD, CEng, FICE, FIMechE, FIStructE (auth.)-Reinforced and Prestressed Concrete-Springer US (1987)

Design of slabs (BS 8110) 327
(a) 0.13% of bh for /y = 460 N/mm 2 ;
(b) 0.24% of bh for /y = 250 N/mm 2 .
Where the control of shrinkage and temperature cracking is important, the
minimum areas should be increased to:
(a) 0.25% of bh for /y = 460 N/mm 2 ;
(b) 0.3% of bh for /y = 250 N/mm 2 •
Comments
(a)
The I.Struct.E. Manual [1] recommends in addition that main bars
should not be less than size 10 and that the percentage of distribution
bars should be at least one-quarter that of the main bars.
(b) With reference to Fig. 8.8-1, suppose the bottom distribution bars
'mark 2' already satisfy the 0.13% requirement (or 0.24%, etc. as the
case may be). Then, according to a strict interpretation of BS
8110: Cl3.12.5.3, the top distribution bars 'mark 1' need only satisfy
the functional requirement of keeping the main top bars in position.
However, the authors share the view that the area of the distribution
reinforcement provided to the main tension bars should be at least
0.13% of bh. For the slab shown in Fig. 8.8-1, the top bars are the
main reinforcement; hence the top distribution bars 'mark 1' should
satisfy the minimum requirement of 0.13%, irrespective of the area of
the bars 'mark 2'.
Concrete cover for durability (BS 8110: Clause 3.3)
Table 2.5-7 in Section 2.5(e) gives the nominal covers to meet the
durability requirements for slabs and other structural members.
Note that in Table 2.5-7 the meaning of nominal cover is as defined in
BS 8110: Clause 3.3.1.1, namely: the nominal cover is the design depth of
concrete to all reinforcement, including links. It is the dimension used in
design and indicated on the drawings.
Fire resistance (BS 8110: Clause 3.3.6)
The fire resistance of a slab depends on its overall thickness and the
concrete cover to the reinforcement, as shown in Table 8.8-1.
Simplified rules for curtailment of bars (BS 8110: Clause 3.12.10.3.1)
The following simplified rules may be used if (i) the loading is predominatly
uniformly distributed, and (ii) for continuous slabs, the spans do
•
2 2 2
Fig. 8.8-1